Silicone heater hose, 39" for cars with the original heater valve bolted on the cylinder head.

Pre 1976 cars can use 2 0f these lengths, commonly known as 1/2" bore heater hose. 

Cars from late 1984 to 1988 had 5/8" outlets on the heater matrix so these hoses will need to be lubricated and pushed on extra hard to fit-originally on these year cars Rover fitted a flared 1/2"hose that was discontinued.